The present invention generally relates to a safety restraint device for protecting vehicle occupants and more particularly a pretensioning or belt tightening device typically used to tension, i.e. tighten, a seat belt wound about a seat belt retractor or attached to that portion of the seat belt connected to a buckle.
Pretensioners or belt tighteners, as they are also called, are currently used in industry to operate in conjunction with seat belt retractors or are attached to one end of the belt that is connected to a seat belt buckle. A typical pretensioner for a seat belt retractor or buckle comprises a movable piston joined to a cable. The piston typically moves down a straight tube. The use of the straight tube creates packaging problems within the vehicle, as it is difficult to orient the tube within the room that is made available. Retractor pretensioners also use clutches to decouple the pretensioner from the retractor so that the pretensioner does not interfere with the normal operation of the retractor. Another type of pretensioner or belt tightener is shown in FIG. 8. This pretensioner 500 includes a gear 502 rotatable with the retractor spool 503. A movable rack having a set of teeth 506 for engagement with the teeth of the gear 502 is disclosed within a longitudinal channel 508 formed in a housing 510. A pyrotechnic unit 512 is disposed below the rack and upon activation pushes the rack upward thereby rotating the gear 502 and causing the spool to reverse wind a seat belt thereon. Even when the rack is moved to its uppermost position, it is still engaged with the gear 502. As can be appreciated, this type of pretensioner or belt tightener must also employ a separate clutch to permit the spool to rotate during normal operation so as to be divorced from the influence of the rack. These clutches typically increase the package size of the restraint device. The clutches are often intricate devices which complicate the operation of the pretensioner and add to its cost. The clutch can be eliminated if the rack (of FIG. 8) is permitted to be pushed into a void in the top of the housing (such that the rack disengages with the teeth of gear 502), however, this would increase the length of the housing. Further, in view of the dimensional tolerances that must be used, the rack of this type of pretensioner is prone to move side-to-side increasing the tooth-to-tooth loading which increases friction, decreases performance, increases noise and may cause the teeth to bind. Additionally, any side loading may cause the rack teeth to bite into the walls of the bore further decreasing performance.
It is an object of the present invention to provide a pretensioner that is devoid of the problems of the prior art. A further object of the present invention is to provide a simple, compact and reliable pretensioner that can be used with a seat belt retractor or a seat belt buckle. Another object of the present invention is to provide a pretensioner or belt tightener which avoids the need to use a separate clutching mechanism.
Accordingly the invention comprises: an apparatus comprising: a spur gear operatively linked to a rotationally supported spool to rotate the spool in a direction of retraction to cause a seat belt wound thereabout to retract; a belt tightener comprising: a gear unit having a first drive member which is initially uncoupled from the driven means and which as it rotates, is placed into driving engagement with the spur gear and which upon further rotation is moved to a condition of disengagement with the spur gear to permit the spool to rotate free of the pretensioner and a rack operably connected to the gear unit means to cause same to rotate.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.